Depends on the game/cheat we are talking about really. Some cheaters try to fool server/other clients. For example in a game of chess, a client can try to move

Depends on the game/cheat we are talking about really. Some cheaters try to fool server/other clients. For example in a game of chess, a client can try to move his pawn like a queen. In this case a server would run the "game simulation" it self and would detect that the client is making an illegal move and a cheater. But this is not always possible/feasible. In an mmo for example it may not be feasible to run physics simulations on server and maybe a server can trust clients when they say "I moved from my old point A to new point B" but in reality there may be a wall in between point A and B Not all cheats are about fooling the server. Some runs on entirely on cheater's side. A board game example would be battleships. A cheater can decide to "look" other side of the board and cheat by looking at opponent's ships. This kind of cheats are solved by only sharing necessary information with clients. For battleships, this would be server only responding the bombing coordinates a client sends and the answer would be a simple "hit/miss". Again, this is not always practical. In a game like counter strike, ideally you would share enemy positions only when they should be visible on someone's screen. But due to lag or not being able to detect this visibility information, a server can choose to always share this information and clients can cheat by presenting that information A harder to catch cheat would be aim hack. In this case a cheater neither fooling the server or benefiting of an information it doesn't have. They usually catch these by checking programs that does this or via player reports or automated systems that catches players that are too good to be legit.